1. Field of the Invention
The present invention relates to a plasma torch electrode, formed from an electrode body that includes a cavity into which an emissive hafnium/zirconium insert is fitted, and to a plasma torch comprising the said electrode.
2. Related Art
The process of cutting structural steels, that is to say non-alloy or low-alloy carbon steels, or even stainless steels and aluminium alloys, by means of a plasma arc in an oxygen atmosphere has been known for many years.
A plasma cutting device capable of implementing such a process generally comprises a plasma cutting torch comprising a nozzle for ejecting the plasma arc towards the workpiece to be cut, an electrode that forms the cathode, placed a certain distance from the nozzle and coaxially therewith, a supply of plasma gas, such as compressed air, oxygen or any other gas mixture containing at least one oxidizing gas, and a means of delivering the plasma gas into the volume separating the electrode from the nozzle, also called a plasma chamber.
The workpiece itself forms the anode, the cathode and the anode being connected to the terminals of a current generator.
To promote the striking of the arc and to limit high-temperature erosion of the electrode in an oxidizing atmosphere, which electrode is typically made of copper or a copper alloy, it is customary to provide the electrode with an emissive insert, made of zirconium or, depending on the case, hafnium, fitted, coaxially, into the end facing the ejection orifice of the nozzle.
Zirconium is a less expensive material than hafnium, but less resistant to high-temperature erosion by the plasma arc.
Conversely, pure hafnium has the best resistance to erosion by the plasma arc, but is very expensive, especially because of the fact that, in order to be able to obtain pure hafnium, it is necessary to “refine” it during its manufacture so as to remove the impurities that contaminate this material.
Although reputed to have a longer lifetime, electrodes provided with an emissive insert made of pure hafnium wear away in a few hours, typically between 2 and 4 hours, when they are used in a plasma cutting torch.
These electrodes with a hafnium or zirconium emissive insert therefore constitute a consumable item of the torch that it is necessary to replace often, which therefore increases the overall cost of the process and poses problems from the industrial standpoint since, to replace the electrode, it is necessary to stop the insulation and dismantle the front part of the torch.
The problem to be solved is therefore how to provide an emissive electrode insert having a lifetime close to that of electrodes with a pure hafnium insert but for a lower manufacturing cost.